Soybean Plants Modify Metal Oxide Nanoparticle Effects on Soil Bacterial Communities

Engineered nanoparticles (ENPs) are entering agricultural soils through land application of nanocontaining biosolids and agrochemicals. The potential adverse effects of ENPs have been studied on food crops and soil bacterial communities separately; however, how ENPs will affect the interacting plant–soil system remains unknown. To address this, we assessed ENP effects on soil microbial communities in soybean-planted, versus unplanted, mesocosms exposed to different doses of nano-CeO₂ (0–1.0 g kg^–1) or nano-ZnO (0–0.5 g kg^–1). Nano-CeO₂ did not affect soil bacterial communities in unplanted soils, but 0.1 g kg^–1 nano-CeO₂ altered soil bacterial communities in planted soils, indicating that plants interactively promote nano-CeO₂ effects in soil, possibly due to belowground C shifts since plant growth was impacted. Nano-ZnO at 0.5 g kg^–1 significantly altered soil bacterial communities, increasing some (e.g., Rhizobium and Sphingomonas) but decreasing other (e.g., Ensifer, Rhodospirillaceae, Clostridium, and Azotobacter) operational taxonomic units (OTUs). Fewer OTUs decreased from nano-ZnO exposure in planted (41) versus unplanted (85) soils, suggesting that plants ameliorate nano-ZnO effects. Taken together, plantspotentially through their effects on belowground biogeochemistrycould either promote (i.e., for the 0.1 g kg^–1 nano-CeO₂ treatment) or limit (i.e., for the 0.5 g kg^–1 nano-ZnO treatment) ENP effects on soil bacterial communities.